1. Field of the Invention
The present invention relates to a magneto resistive (MR) head, and in particular, to a technique for optimizing an MR-bias current by measuring an amplitude of a signal read through an MR-head.
2. Description of the Related Art
A magnetic disk storage, such a hard disk drive, normally employs an MR-head, with an increase in the storage capacity. The MR-head is composed of a thin film head and a MR-sensor for data reading. The MR-sensor changes a resistance according to a change of the magnetic flux from a storage medium, and the change of the resistance is expressed as a read signal. Further, the MR-sensor is provided with a bias current to express the change of the magnetic flux as the read signal. The bias current supplied to the MR-head should be set such that the read signal should be linear with respect to the change of the magnetic flux. Improper setting of the MR-bias current may cause asymmetry and baseline shift of the read signal.
When the MR-bias current is set to an optimal value, the positive and negative pulses of the read signal from the MR-sensor are symmetrical with respect to the base line. However, when the MR-bias current is improperly set, the base lines are shifted up and down, causing an asymmetry of the read signal and a signal component adjacent to the shifted base line may be erroneously considered to be normal data, resulting in a data read error.
The following patents each disclose features in common with the present invention but do not teach or suggest the specifically recited technique for optimizing the MR-bias current in accordance with the present invention:
U.S. Pat. No. 5,719,716 for METHOD OF AND DEVICE FOR AUTOMATIC BIAS CONTROL issued to Suzuki, U.S. Pat. No. 5,719,719 for MAGNETIC DISK DRIVE WITH SENSING CURRENT ADJUSTMENT OF MR HEAD issued to Tsuyoshi et al., U.S. Pat. No. 5,774,291 for VOTAGE MEASUREMENT CIRCUIT FOR A MAGNETORESISTIVE HEAD INSTALLED IN A DISK ENCLOSURE issued to Contreras et al., U.S. Pat. No. 5,831,782 for METHOD AND APPARATUS FOR SUPPLYING OPTIMAL BIAS CURRENT TO A MAGNETIC HEAD issued to Kohno et al., U.S. Pat. No. 4,050,086 for DYNAMIC TRANSDUCER BIASING SIGNAL AMPLIFYING CIRCUITRY issued to Harr, U.S. Pat. No. 5,301,080 for BIAS SERVO LOOP FOR MAGNETO-RESISTIVE READ/WRITE HEAD issued to Ottesen et al., U.S. Pat. No. 5,309,295 for METHOD AND APPARATUS FOR BIASING A MAGNETO-RESISTIVE HEAD issued to Bailey et al., U.S. Pat. No. 5,367,411 for MAGNETIC RECORDING AND REPRODUCING APPARATUS WITH REPRODUCING HEAD OF MAGNETORESISTIVE TYPE HAVING CONTROL OF MAGNETIC BIAS LEVEL issued to Nishiyama et al., U.S. Pat. No. 5,390,054 for METHOD AND SYSTEM FOR MINIMIZING THE ERROR RATE OF A DIGITAL RECORDING SYSTEM BY PREDICTING THE OPTIMAL BIAS CURRENT issued to Youngquist et al., U.S. Pat. No. 5,196,967 for METHOD OF AUTOMATICALLY OPTIMIZING THE RECORDING BIAS FOR A VIDEO SIGNAL, AND ARRANGEMENT FOR CARRYING OUT THE METHOD issued to Mederer et al., U.S. Pat. No. 4,528,602 for ELECTRICAL CALIBRATION ARRANGEMENTS issued to Crick et al., U.S. Pat. No. 4,553,179 for AUTOMATIC RECORDING BIAS CURRENT SETTING APPARATUS issued to Inami et al., U.S. Pat. No. 4,611,253 for MAGNETIC RECORDING AND REPRODUCING DEVICE issued to Kamei et al., U.S. Pat. No. 4,616,273 for TAPE RECORDING APPARATUS PROVIDED WITH A BIAS CONTROL DEVICE issued to Ishii et al., U.S. Pat. No. 4,297,730 for MAGNETIC RECORDING AND REPRODUCING DEVICE issued to Kakowaki et al., U.S. Pat. No. 4,344,094 for METHOD AND APPARATUS DETECTING AND SETTING OPTIMUM TAPE RECORDING BIAS issued to Ohtake et al., U.S. Pat. No. 4,379,311 for RECORDING BIAS SETTING DEVICE FOR A MAGNETIC RECORDING AND REPRODUCING APPARATUS issued to Ohkawara, U.S. Pat. No. 4,220,979 for BIAS LEVEL SETTING CIRCUIT FOR TAPE RECORDERS WITH STAIRCASE HIGH FREQUENCY SIGNAL issued to Kitamura et al., U.S. Pat. No. 4,245,265 for AUTOMATIC TAPE BIAS ADJUSTING AND SIGNAL COMPENSATION RECORDING AND REPRODUCING APPARATUS issued to Kogure et al., U.S. Pat. No. 4,262,313 for BIAS CURRENT SETTING APPARATUS IN A MAGNETIC RECORDING AND REPRODUCING APPARATUS issued to Mouri, and U.S. Pat. No. 4,280,153 for DIGITALLY CONTROLLED AUTOMATIC BIAS CIRCUIT FOR MAGNETIC RECORDING issued to Tin.